Many, many people are unhappy with Gutenberg (including me). Gutenberg still has a lot of bugs that still need to be worked out. It was prematurely released.
A potential solution would be to fix the spacer so that the smallest setting is the same as a line space. People could just use the spacer when nothing else works.
I tried to find a way to change the default font size in the theme but so far have been unable to find anything. I may try to contact the theme author to see if I can get some support.
